Scalable, electro-optically induced force system and method

ABSTRACT

A technique is disclosed for electro-optically inducing a force to fabricated samples and/or devices with laser light. The technique uses the interaction of the oscillating electric field of the laser beam in opposition with the electric field produced by an appropriate electric charge carrier to achieve a net repulsive (or attractive) force on the component holding the electric charge. In one embodiment, force is achieved when the field near the charge carrier is modulated at a subharmonic of the electric field oscillation frequency of the laser and the relative phases of the light field and electric charge carrier field are controlled to provide optimal repulsion/attraction. The effect is scalable by applying the technique to an array of charge carrier fields sequentially as well as using higher power lasers and higher carrier field voltages.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of, and claims the benefitunder 35 U.S.C. § 120 from, nonprovisional U.S. patent application Ser.No. 16/420,162, entitled “Scalable, Electro-Optically Induced ForceSystem And Method”, filed May 23, 2019. Application Ser. No. 16/420,162,in turn, is a continuation-in-part of, and claims the benefit under 35U.S.C. § 120 from, nonprovisional U.S. patent application Ser. No.15/959,280, entitled “Scalable, Electro-Optically Induced Force SystemAnd Method”, filed Apr. 23, 2018, now U.S. Pat. No. 10,354,772.Application Ser. No. 15/959,280, in turn, is a continuation-in-part of,and claims the benefit under 35 U.S.C. § 120 from, nonprovisional U.S.patent application Ser. No. 15/406,737, entitled “Scalable,Electro-Optically Induced Force System And Method”, filed Jan. 15, 2017,now U.S. Pat. No. 9,984,782. The subject matter of each of the foregoingdocuments is expressly incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to techniques for applying aforce or inducing a change in momentum to objects using interactingelectromagnetic fields and, particularly, to techniques for applying aforce or inducing a change in momentum to objects using a laser beam asone of the sources of the electromagnetic fields.

BACKGROUND INFORMATION

The manipulation of samples or devices through the use ofelectromagnetic (EM) radiation has a number of advantages overmechanical or “tactile” manipulation.

Typically, EM manipulation is less mechanically destructive and can beaccomplished through mechanical barriers where other more traditionalmeans are not effective. EM manipulation has become more prevalent astechnology has advanced and is now accomplished through both constantfield applications (as in the case of superconductor facilitatedmagnetically induced levitation) and oscillating field applications(e.g. laser assisted cooling and trapping).

The manipulation of mass through the use of laser light has found manyapplications as laser technology has evolved. Not simply laserphotolysis or spectroscopy, but coherent control of chemical reactionsis becoming possible (see P. Brumer and M. Shapiro, Sci. Am., pg. 56,March 1995). Laser atom or molecule trapping has seen a great deal ofactivity (see S. Chu, Science, pg. 861, 23 Aug. 1991; C. N.CohenTannoudji and W. D. Phillips, Phys. Today, pg. 33, October 1990)and has lead to the observation of Bose-Einstein condensation and theimprovement of atomic clocks. Control of larger mass samples with laserenergy has also been demonstrated. “Optical tweezers” have been used tostretch single strands of DNA and manipulate chromosomes inside cellnuclei and move entire cellular organelles without destroying the cellwall (see S. Chu, Sci. Am., pg. 71, February 1992). Standing wave laserradiation has also been used to deflect atomic beams in flight (see P.E. Moskowitz, P. L. Gould, and D. E. Pritchard, J. Opt. Soc. Am. B., 2,11, 1784, 1985).

All of these techniques allow for control of small samples with laserlight, but none of these is practically applicable to larger samples orefficiently uses the laser light to accomplish the manipulation. One ofthe difficulties is that many of the current techniques operate byinducing an electric charge polarization in the sample. The force whichcan be induced by the laser beam is directly related to the degree towhich a sample can be polarized before it is damaged. The laser peakintensity must be controlled or the sample can be overheated, ionized ordestroyed. This limits the achievable manipulation force. Also, thesetechniques commonly require the laser to be focused on the targetsample, limiting the length of interaction and thus the efficiency withwhich the laser energy is coupled into translation. Other techniquesrely on the transfer of photon momentum in the optical scatteringprocess, but this is extremely inefficient as photons at commonlyaccessible wavelengths have very little mass.

Therefore, it is the object of the present invention to provide a systemthat 1) employs laser light to apply a force to objects that 2) isscalable, that 3) maximizes the efficiency with which the laser light isutilized for said force, that 4) the intensity of laser light employedby the system should not be limited by the risk of damage to the objectupon which the force is induced.

SUMMARY

The essence of electro-optically induced force and/or momentum is tomimic the repulsion manifested when two like charged wires come intoproximity with one another. Wires carrying like charges repel oneanother due to the mutual opposition of the electric fields generated bythe charges on the wires. An electro-optically induced force is realizedwhen one of the wires is replaced with a substitute that maintains anelectric field in opposition to the field generated by the first wire(e.g. a photon or radiation field). The principles employed by thepresent invention to electro-optically induce a force to manipulateobjects are now described.

FIG. 1 shows a schematic of 1) the electric field around an electricallycharged wire parallel to the Z-axis (i.e. perpendicular to the page ofthe schematic) (100), 2) the projection of said electric field on theY-axis (vertical in the plane of the page), said projection is describedby a sine function (102), 3) the electric field of a laser beampropagating in space perpendicular to the wire, 1) above (104), 4) theelectric field of a laser beam retro reflected by a mirror with asurface perpendicular to the laser beam path (106).

FIG. 2 shows a schematic of the field interaction, in space at a giveninstant, between the electric field from a charged wire (200) and theelectric field of a laser beam travelling proximate and perpendicular tothe charged wire (202) (i.e. for those fields illustrated in FIG. 1). Itshould be noted that, in the case of a freely propagating laser, acontinuous sine wave, and the Y-axis component of the electric fieldshown, a second sine wave, the net field interaction will always bezero, a function of the orthogonality of sine functions. But, in thecase of a retro reflected laser beam, by positioning the retroreflecting mirror judiciously, the spatial relationship between thestanding electric field of the wire (200) and the electric field of thelaser (202) and can be chosen so the net field interaction between theelectric field of the laser and the electric field near the wire, at thegiven moment illustrated, is non-zero. The net field interaction (204)is shown schematically in FIG. 2.

It should be noted that the spatial relationship between the electricfield of the laser and the standing electric field near the wire can bealtered, and a non-zero net field interaction achieved, usingtransmissive optics as well. A schematic is shown in FIG. 3. In thiscase, the change in refractive index, n, between the originalpropagation medium (e.g. air, for which n ˜1) and the medium of theoptic (e.g. glass, for which n ˜1.5) gives rise to a phase changebetween the electric field near the wire along the propagation directionof the laser (300) and the electric field of the laser (302). Thischanges the integral of the interaction between the two electric fields(304) to a, potentially, non-zero value.

A final case is shown schematically in FIG. 4. The spatial relationshipbetween the electric field near the wire (400) and the electric field ofthe laser (402) is altered by directing the laser through an aperture ofan electrically conductive material. In such a case the conductivematerial screens the electric field near the wire (400) from interactionwith the electric field of the laser (402) internal to the conductivematerial. This changes the integral of the interaction between the twoelectric fields (404) to a, potentially, non-zero value.

The above describes methods for achieving a non-zero net fieldinteraction at a given moment in time, meaning a given phase of thelaser light, but the electric field of a laser oscillates at frequencygiven by f=c/λ, where c is the speed of light and λ is the wavelength ofthe laser. This frequency is typically hundreds of terahertz, muchfaster than practical electronic signals can be generated, and so anymomentary interaction between the laser and the standing electric fieldof the wire will quickly integrate to zero. In order to sustain andextend a net field interaction over time, it is necessary to vary theelectric field near the wire.

FIG. 5 shows a schematic of the interactions, in time, between theelectric field near a wire driven by a square waveform (500) and theelectric field of a laser beam traveling proximate and perpendicular tothe wire (502). The accumulated field interaction (504) over one periodof the waveform driving the charge on the wire is given byF=∫ sin(ω_(l)(t))*f _(sg)(t,θ _(pm))∂t  Eq. 1and is shown schematically in FIG. 5. Where, ωl is the frequency of thelaser beam, fsg is the time-variant electric field near the wire, andθpm is the value of the time-variant optical phase modulation induced tothe electric field near the wire.

It should be noted that, 1) depending on the relative phase of the givenelectric fields, the above integral (eq. 1) can be either positive ornegative, corresponding to the case of generating a repulsive orattractive force, respectively and 2) although the waveform shown inFIG. 5 is a square wave, that need not be the case. Since the signaldriving the electric field on the wire cantilever is electronicallygenerated, fsg can be configured as any function that is determined tofacilitate the desired effect. Note is given to the case of a phasemodulated sine wave.

Consider a specific case: a signal generator operating at 5.64 GHz andcommon laser wavelength, 532 nm or ˜5.64×1014 Hz. In this case, thelaser is operating at a frequency that is one hundred thousand timesfaster than the signal generator. In this example, the electric field ofthe laser and the electric field induced near the wire may only be inopposition, in time, space, and intensity, a fraction measured in partsper million (ppm) depending on the specific wave shape and/or modulationinduced to the electric field near the wire. But, as described below, afield carrier array may be constructed with very high density, withfeature spacing in the sub-micron range. In such a case, one couldachieve one million, or more, field interaction locations per meter, andso, even if the electric field of the laser and the electric field nearthe charge carrier are in opposition a small fraction of the time peroscillation at each location, integrating one million locations over thelength of a one meter array, comprised of one million elements, canafford substantial accumulated force between the electric field of thelaser and the electric field(s) near the array.

The teachings of the present invention are operable in systems where theelectric fields are neither free-space nor produced by a laser. Thepresent invention is generally directed to any electro-optical systemincluding a charge carrier configured to carry a charge distributionthat gives rise to a first electromagnetic field, and a radiation sourceconfigured to generate a second electromagnetic field that interactswith the first electromagnetic field so as to produce a net force on thecharge carrier.

Further details and embodiments and methods are described in thedetailed description below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and features of the invention will be more readilyapparent from the following detailed description and appended claimswhen taken in conjunction with the drawings, in which:

FIG. 1 is a schematic diagram illustrating the electric fields employedin the present invention.

FIG. 2 is a schematic diagram illustrating phase relationship betweenthe electric fields employed in the present invention, retro-reflectingcase.

FIG. 3 is a schematic diagram illustrating phase relationship betweenthe electric fields employed in the present invention, transmissiveoptic case.

FIG. 4 is a schematic diagram illustrating phase relationship betweenthe electric fields employed in the present invention, conductivescreening case.

FIG. 5 is a schematic diagram illustrating the variations, in time,between the electric field of the laser and the electric field near thecharge carrier, as well as the accumulated field product integral,representing the accumulated force on the carrier.

FIG. 6 is a schematic of a circuit that is configured to process acommercially available square wave into a signal sufficient to induce ameasurable force between a continuous wave single frequency laser and aconductive wire cantilever.

FIG. 7 is a schematic diagram illustrating a first preferred embodimentof the present invention employing a continuous wave single frequencylaser and a single field carrier.

FIG. 8 is a schematic diagram illustrating a preferred embodiment of thepresent invention employing a continuous wave single frequency laser anda field carrier array.

FIG. 9 is a schematic diagram illustrating the relationship between theelectric fields employed in the present invention, free space case.

FIG. 10 is a schematic diagram illustrating a preferred embodiment ofthe present invention employing a continuous wave single frequency laserand a field carrier array, free space case.

FIG. 11 is a schematic of a circuit that is configured to process acommercially available sinusoidal signal into a signal sufficient toinduce a measurable force between a continuous wave single frequencylaser and a conductive wire cantilever: combiner case.

FIG. 12 is a schematic of a circuit that is configured to improve thenoise/jitter of a commercially available sinusoidal signal generator.

FIG. 13 is a schematic of a circuit that is configured to process acommercially available sinusoidal signal, reducing the noise/jitter,into a signal sufficient to induce a measurable force between acontinuous wave single frequency laser and a conductive wire cantilever.

FIG. 14 is a schematic illustrating two co-propagating lasers forming apulse train

FIG. 15 is a schematic illustrating the effect of self-phase modulationon an optical pulse. The phase of the center area of the pulse isdelayed with respect to the outer edges of the pulse.

FIG. 16 shows schematics of the laser electric fields in the single modeand pulsed cases.

FIG. 17 shows schematics of the laser electric fields in the single modeand pulsed cases, as well as a schematic of the phase modulation, underconditions where phase modulation is present.

FIG. 18 shows schematics of the laser electric fields in the single modeand pulsed cases, as well as schematics of the phase modulation andspace and time integrals, under conditions where phase modulation anddispersion are present.

FIG. 19 is a schematic diagram illustrating an embodiment of the presentinvention employing four continuous wave single frequency lasers and asingle charge carrier.

FIG. 20 shows a gray-scale image of the electric field of a propagatinglaser in both space and time.

FIG. 21 shows a gray-scale image of the electric field of a propagatinglaser in both space and time, when dispersion is present.

FIG. 22 shows a gray-scale image of the electric field of a propagatinglaser in both space and time, when dispersion and phase modulation arepresent.

FIG. 23 shows a gray-scale image of the electric field of a propagatinglaser in both space and time, when dispersion and more exaggerated phasemodulation are present.

FIG. 24 shows a gray-scale image of the electric field of a propagatinglaser in both space and time, when dispersion and phase modulation arepresent, and an example of how charge carriers may be placed, along the‘x’ direction, to achieve a net force from the non-zero, time-integratedelectric field.

FIG. 25 is a flowchart of a method 2000 in accordance with another novelaspect.

FIG. 26 is a flowchart of a method 2100 in accordance with another novelaspect.

DETAILED DESCRIPTION

Reference will now be made in detail to some embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings.

The present invention allows for the application of laser light toachieve a scalable electromagnetically induced force to samples ofgreater mass than previous techniques and for more efficient use of theapplied laser light. The sample upon which the force is realized must beof specific construction to support an electric charge distribution andvariation to achieve a net repulsion or attraction with the laser light.Using this approach the laser need not be focused on the sample norinduce an electric charge polarization on the sample. This allows theforce to be integrated over a longer distance, greatly improving theefficiency with which the laser energy is used and increasing the massamenable to manipulation by the techniques of the present invention.

Several recent advancements have driven this invention. First, the laserpower available from smaller, less expensive devices is increasingcontinually. Laser devices are now being constructed that produce wattsof laser energy from laser heads that are millimeters or evenmicrometers in size.

As for the magnitude of the accumulated force, let us consider theexample of a 10 W laser. Currently such lasers can be fabricated atrelatively low cost, and weigh on the order of grams. Ten Watts (10N*m/s) of optical power, if converted entirely to work (N*m) could lift1 kg of mass 1 meter per second against earth's gravity (9.8m/s{circumflex over ( )}2). An array of one thousand 10 W lasers, or thecase of a single 10 kW laser, could potentially lift tons.

It is the object of this invention to be scalable and to enable suchapplications.

Second, laser energy efficiency is improving as technology advances. Asan example, 35-60% of the energy spent to drive some laser diodes isconverted directly to laser light energy.

Third, circuit features smaller than 0.25 micrometers can now befabricated and this technology continues to advance to fabricatefeatures of even smaller size. This feature size is less than half thewavelength of light produced by many high power laser packages. Thisprovides an excellent opportunity to construct a periodic chargedistribution giving rise to a periodic electric field that can directlycounter the periodic electric field of a laser beam. This is an idealarrangement for electromagnetic repulsion/attraction (i.e.,electro-optically induced force).

Single Frequency Laser Source Embodiments

Signal Generator System

FIG. 6 shows a schematic of a circuit used to process a commerciallyavailable square wave into a signal sufficient to induce a measurableforce between a continuous wave single frequency laser and a conductivewire cantilever. A square wave signal generator (600) is set to generatea drive signal at a subharmonic of the laser frequency (e.g. one hundredthousandth of the laser frequency). The output of the signal generatoris directed through an adjustable delay line (602). It is advantageousto drive the signal at higher voltage since the field interactionssought scale with the field intensity and thus voltage applied. Thesignal can be amplified using a broadband amplifier (604) to increasethe net force induced.

Commercially available signal sources (e.g. square wave clockgenerators) may have signal jitter in the 100 to 300 femtosecond range,but the laser electric field oscillation for commercially availablesingle frequency lasers (e.g. a 532 nm laser) is approximately 2femtoseconds. In such a case, the jitter of the square wave willpreclude any efficient induction of force on the wire cantilever as itwill tend to average out any net repulsion/attraction. It is necessaryto improve the square wave signal jitter to provide for stable andefficient field interactions. To accomplish this, the processed squarewave signal, described above, is directed into the forward port of abroadband directional coupler (606). The output of the directionalcoupler is sent to a third adjustable delay line (608) and back to theinput port of the broadband coupler (606), creating a loop. The delayline (608) is adjusted to phase lock the resultant signal loop. Ineffect the delay line (608) is adjusted to ensure that the signal loopis an integer multiple of the square wave length. In such anarrangement, the jitter of the input signal is reduced by the squareroot of the number of round trips the signal makes in the loop. In thecase of a 40 db power coupler, the jitter is improved by a factor of 10.

To improve the signal jitter further, the signal from the reference portof the broadband coupler (606) is directed to the forward port of asecond broadband coupler (610). The output of the second broadbandcoupler (610) is directed through a fourth delay line (612) and back tothe input port of the second broadband directional coupler (610). Thedelay line (612) is adjusted to phase lock the second resultant signalloop. In effect the delay line (612) is adjusted to ensure that thesecond signal loop is also an integer multiple of the square wavelength. Again, the jitter of the input signal is reduced by the squareroot of the number of round trips the signal makes in the second loop.In the case of a 40 db power coupler, the jitter is improved by afurther factor of 10.

In the above description, two successive directional coupler stagesshould be sufficient to reduce the (e.g. 200 fs) jitter of the squarewave clock generator source to a value comparable to the oscillationfrequency of the single frequency laser source (approximately 2 fs), butsuccessive stages of broadband couplers and paired delay lines can beemployed to reduce the jitter to desired levels.

In this embodiment, the wire cantilever configured to achieve arepulsion with the single frequency laser, below, is within the secondcoupler (610)/delay line (612) loop described above. The interactionsite (614) is shown schematically in FIG. 6. The signal from thereference port of the second directional coupler (610) is directed to amonitor oscilloscope (616).

FIG. 7, shows a schematic of a preferred embodiment. A continuous wave(CW) single frequency laser (700) produces a beam (702) that is directedto a retro-reflecting mirror (704) to provide the opticalelectromagnetic field which will induce a force at the wire cantileversite (614) described above and shown schematically in FIG. 6. The squarewave clock generator (706), signal processing circuit (708), and monitoroscilloscope (710) are the same as those described in FIG. 6, (600),(602-612), and (616), respectively. The wire cantilever (712) consistsof a length from the second directional coupler (610)/delay line (612),above, configured to be in close proximity (e.g. less than 1 mm) to thelaser beam (702) and retro-reflecting mirror (704). The system isconfigured such that the linear polarization of the laser beam (702) isperpendicular to the wire cantilever (712).

Interferometric Force Detection System

A fiber optic force detection system similar to that used in atomicforce microscope studies (D. Rugar, H. J. Mamin, and P. Guethner, Appl.Phys. Lett. 55, 25, (1989) 2588) is employed here to measure forceinduced between a wire cantilever loop (712) and a laser beam (702).

The output of a single-mode fiber-coupled probe laser (714) is directedinto a single mode 2×2 fiber coupler (716). One optically cleaved end ofthe output fiber (718) of the fiber coupler (716) is positioned in closeproximity (e.g. single microns) and perpendicular to the wire cantilever(712). A piezo electric actuator, PZT (720) is attached to the opticalfiber (718) and driven by a signal generator (722). The PZT (720) drivesthe motion of the optical fiber (718) perpendicular to the wirecantilever (712).

The single frequency laser light exiting the output of the fiber coupler(718) is made incident upon the wire cantilever (712). A portion of thelight exiting the optical fiber (718) and incident on the wirecantilever (712) is reflected back into the optical fiber (718) andco-propagates with the light reflected from the internal surface of theoptically cleaved fiber (718).

The return signal, the optical interferometric signal between thecounter propagating reflection of the optically cleaved end of theoptical fiber (718) and the reflective surface of the wire cantilever(712), travels back through the optical fiber (718), back through thefiber coupler (716), and is directed into a detector photodiode (724).The output of the detector photodiode (724) is measured using a lock-inamplifier (726), using the reference signal from the signal generator(722) driving the PZT (720). The signal from the lock-in amplifier isobserved on a monitor oscilloscope (728). A monitor photodiode (730) canbe employed to measure the second output of the fiber coupler (716) toensure system stability.

The constructive and destructive interference between the lightreflected from the internal surface of the optically cleaved fiber (718)and the light reflected from the wire cantilever (712), driven anddetected at the frequency of the lock-in amplifier (726), allows for avery sensitive detection of movement of the wire cantilever (712) (e.g.nanometers). When the wire cantilever (712) is chosen with a small forceconstant, this allows for very sensitive force detection (e.g.nanoNewtons).

Laser/Carrier Field Interaction

The choice of frequency of the square wave generator (706) is criticalfor manifestation of the desired effect. FIG. 5 shows a condition wherethe laser frequency (502) is an odd multiple of the cantilever driverfrequency (500). In such a case, the positive, rising, half cycle of thesquare wave is integral over an extra (e.g. positive) half cycle of thelaser oscillation and the negative, falling, half cycle of the squarewave is integral over a complimentary (e.g. negative) half cycle of thelaser oscillation. This frequency, and phase, relationship gives rise tocumulative, non-zero, field interaction (504) between the electric fieldof the laser (502) and the electric field near the wire cantilever (500)over time.

It has been noted, above, that depending on the relative phase of thegiven electric fields, the above integral (eq. 1) can be either positiveor negative, corresponding to the case of generating a repulsive orattractive force, respectively, on the wire cantilever. In the presentcase, the relative phase between the oscillating electric field of thelaser (700) and the oscillating electric field of the wire cantilever(712) can be easily achieved by adjusting the delay line of the signalprocessing circuit (602).

Carrier Array

FIG. 8 shows a schematic where a set of field carriers (e.g. a set ofwire cantilevers, or alternatively a series of traces on a printedcircuit board) (832) is arrayed perpendicular to and along a laser's(800) propagation path (802) and an equivalent set of transmissiveoptics (804) is paired with each field carrier to facilitate theprocess, as shown schematically in FIG. 3. The field carriers shown(834) share a common platform, so a single interferometric detectionmeasurement (814-830), as shown in FIG. 7, is sufficient to measure thecumulative force on the ensemble of field carriers.

As the circuit path for each carrier is unique, each field carriersignal wave must have separate phase control to facilitate the desiredeffect. The phases are adjusted to maximize the force detected via theinterferometric detector signal described above.

While the preferred embodiments, above, employ a single frequency laser,the techniques of the present invention are applicable to multi-modelasers.

Multi-Mode Laser Embodiment

Typically, lasers that provide high output power operate in severallongitudinal modes of the laser resonator cavity. The wavelengths of thecavity modes of any laser are given by the expression: n I=2 L, where, nis an integer, I is the wavelength of the laser light, and L is thelength of the laser resonator cavity. As a result, when a multi-modelaser is used several different wavelengths of laser light are producedsimultaneously.

Therefore, the present invention also includes an embodiment that usesthe laser light from multi-mode lasers by providing a path to match eachof the laser's active laser cavity modes.

Free Space Laser Propagation Embodiment

It should be noted that the electric field near a set of charge carrierscan be configured such that a non-zero net interaction with the electricfield of the laser can be achieved, in the case where the laser isdirected to travel proximate and perpendicular to the charge carriers infree space, with no optics in the laser beam path. A schematic is shownin FIG. 9. In this case, the charges on a set of separate carriers (e.g.a set of parallel traces on a PCB) are configured to achieve anon-sinusoidal electric field variation in the direction of laser travel(900). The electric field of the laser beam (902) is shown schematicallyover the same distance. In such a case, the space integral (904) of theelectric field near the charge carrier array (900) and the electricfield of the laser (902) can be a non-zero value.

FIG. 10 shows a schematic where a set of field carriers (e.g. a set ofwire cantilevers, or alternatively a series of traces on a printedcircuit board) (1032) is arrayed perpendicular to and along a laser's(1000) propagation path (1004). The field carriers shown share a commonplatform (1034), so a single interferometric detection measurement(1014-1030) is sufficient to measure the cumulative force on theensemble of field carriers.

As the circuit path for each carrier (1032) is unique, each fieldcarrier signal wave must have separate phase control to facilitate thedesired effect. The phases are adjusted to maximize the force detectedvia the interferometric detector signal described above.

Jitter Reduction Circuit with Combiner Embodiment

FIG. 11 shows a schematic of an alternate embodiment of a circuit toreduce jitter in an electronic signal, the first embodiment having beenpresented in FIG. 6. In FIG. 11, a sinusoidal signal generator (e.g. 1GHz, 300 fs jitter) (1100) is directed into a first input port of afirst signal combiner (1102). The first signal combiner (1102) providesan isolation (e.g. 40 db) between the two input ports of the combiner(1102). The output of the first combiner (1102) is directed into thefirst input port of a, similar, second combiner (1104). The output ofthe second combiner (1104) is directed to the input of a firstadjustable delay line (1106) and the output of the first delay line(1106) is directed into the second input port of the first combiner(1102), thereby creating a feedback loop that propagates through thefirst delay line (1106). When the delay line (1106) is adjusted suchthat the length of one round trip through the circuit (1102, 1104, and1106) is an integral multiple of the wavelength of the signal from thesignal generator (1100), the feedback loop serves to reduce both thejitter and amplitude noise of the input signal by the square root of thenumber of round trips through the circuit, determined by the isolationvalues of the combiners (1102 and 1104). As an example, if the combinersserve to transmit ninety nine percent of the signal from the firstcombiner input port to the combiner output port and one percent of thesignal exits through the second input port of the combiner, a result ofimperfect isolation, the number of round trips through the feedback loopwould be approximately ninety eight. In such a case the noise in theabove circuit would be reduced by the square root of approximatelyninety eight, or nearly ten-fold.

In FIG. 11, a second combiner set is shown (1108 and 1110). The purposeof the second combiner set (1108 and 1110) is to reduce the signal noisefurther. The signal from the second input of the second combiner (1104),the leakage from the second combiner, is directed to the first inputport of a third signal combiner (1108). The output of the third combiner(1108) is directed to the first input port of a fourth combiner (1110)and the output of the fourth combiner is directed to the input of asecond adjustable delay line (1112). The output of the second delay line(1112) is directed to the second input of the third signal combiner(1108), thereby creating a second feedback loop. The length of thesecond feedback loop is adjusted to be an integral multiple of thewavelength of the signal from the signal generator (1100). Thus thesecond set of combiners (1108 and 1110) and the second delay line (1112)serve to further reduce the signal noise from the output of the secondsignal combiner (1104) (e.g. by a further factor of 10)

The signal, leakage, from the second input port of the fourth signalcombiner (1110) is directed to a commercial circuit (1114) that convertsa sinusoidal signal to a square wave signal, thus providing the signalupon the charge carriers in FIGS. 7, 8 and 10 (712, 812/832, and1012/1032, respectively) sufficient to induce a measurable force betweena continuous wave single frequency laser and a conductive charge carrieror series of charge carriers.

FIG. 12 is a schematic of a circuit that is configured to improve thenoise/jitter of a commercially available sinusoidal signal generator. Inthe embodiment of FIG. 11, the circuit employs high discrimination (e.g.40 dB) splitter/combiners to improve the noise/jitter on a periodicelectrical signal. In the embodiment of FIG. 12, low discriminationsplitter/combiners (e.g. 3 dB) are employed to achieve a similar resultas in the embodiment of FIG. 11. The signal from a signal generator(1200) is directed into a circuit with 2 inputs (1202 and 1204) and 2outputs (1206 and 1208), where the second output is directed to thesecond input and connected thereto by a delay line (1210). In the casein FIG. 12, the internal circuit consists of 2 beam splitters (1212)(e.g. 3 dB). When the circuit is configured such that each potentialpath available to the input signal is an integer multiple of thewavelength of the input signal, the circuit will reduce the noise/jitterin the input signal by the square root of the additive waves. In thecase of FIG. 12, assuming 3 dB splitter/combiners, ˜⅔ of the inputsignal would be transmitted to the first output and the noise/jitter ofthe output signal would be ˜15% lower than the noise/jitter of the inputsignal.

In one embodiment, the distance of the electrical paths between the twosignal splitters is not equal. Rather, one side is a non-zero integermultiple of the input signal wavelength longer than the other. In such acase the noise/jitter reduction of the output signal would be greater,˜50% in the present case.

FIG. 13 shows another embodiment of the noise/jitter reduction circuit.The signal from a signal generator (1300) is directed into a circuitwith 2 inputs (1302 and 1304) and 2 outputs (1306 and 1308), where thesecond output (1308) is directed to the second input (1304) andconnected thereto by a delay line (1310). In the case in FIG. 13, theinternal circuit consists of a multiplicity of signal splitter/combiners(1312) (e.g. 3 dB) arranged such that each circuit path available to theinput signal is an integer multiple of the wavelength of the inputsignal. In such a case, the signal can be split a multitude of times,each split signal element traveling along a circuit path that is aninteger multiple of the wavelength of the signal, and recombined withother split elements a multitude of times, each recombination eventaveraging out and reducing the noise/jitter of the signal. The signal atthe first output of the circuit can see substantial (e.g. >100 fold)decrease in the noise/jitter when compared to the input signal.

In one embodiment, the distance of the electrical paths within the arrayof signal splitters are not uniform. Rather, the distances are anon-zero integer multiple of the input signal wavelength. In such anembodiment, the noise/jitter reduction efficiency of the circuit wouldbe improved due to the improved variance in the recombination process.That is, each recombination would tend to occur with a signal elementmore widely distributed throughout the signal chain.

Field Phase and Amplitude Induced Modulation Embodiments

In prior embodiments, a force between a radiation field, a laser, and acharge carrier is achieved by varying the charge on the charge carrierin a manner that is synchronous with the oscillation of the electricfield of the laser beam. In another embodiment, an appropriatemodulation is induced to the laser field phase and amplitude and thecharge on the charge carrier is held constant. This approach can improvethe efficiency of the force generation as well as the cost andmanufacturability of devices using the approach to achieve forcegeneration.

In this additional embodiment, two or more sources of radiation areemployed. For the sake of simplicity, the first case is described wheretwo laser sources are employed. For example, one 1550 nm laser sourceand one near 1300 nm laser source. These values are selected for severalreasons related to commercial availability, including 1) they are commonin the telecommunications industry, 2) they can be very low cost ($5),3) their power can be quite high (200 mW), and 4) they can bemanufactured to be extremely small (<<1 mm{circumflex over ( )}2)

There are three optical phenomena that are required to achieve thesynergistic laser amplitude and phase modulation necessary to generate aforce on a charge carrier with a constant charge: 1) optical pulsing, 2)the optical Kerr effect, and 3) optical dispersion.

Optical Pulsing

In the current case, optical pulsing is achieved by co-propagating twolasers of different wavelengths (e.g. 1550 nm and 1300 nm). FIG. 14shows a schematic of the electric fields generated when two lasers, ofdifferent wavelengths, are combined, made collinear, and directed topropagate in the same direction. Because of the differences inwavelength, the two lasers oscillate between the states where they arein-and-out of phase, the amplitude envelope oscillating between zero andone. This creates a pulse train, the pulse rate of which is determinedby the wavelength spacing between the two lasers.

Optical Kerr Effect

Many optical media (e.g. optical fibers used in the telecommunicationsindustry) manifest the optical Kerr effect, the phenomenon wherein theoptical index of the medium (the speed at which light travels throughthe medium) is a function of the intensity of the light itself. Whenvery high intensity light is used (e.g. laser light) this change to theoptical index can become substantial.

In the case of optical pulses, the Kerr effect often gives rise to‘self-phase modulation.’ This phenomenon distorts the pulse as shown inFIG. 15, wherein the phase modulated pulse (1500) is offset from theunmodulated pulse (1502). The leading and trailing edges of the opticalpulse, the low intensity parts of the pulse, experience a lower index ofrefraction and thus travel more quickly through the medium than thecenter part of the optical pulse, the higher intensity part of thepulse, which experiences a higher index of refraction and thus travelsmore slowly through the medium.

Optical Dispersion

Optical dispersion is the phenomena wherein different wavelengths oflight travel through a given medium at different speeds. This isdistinguished from the Kerr effect above in that it is not, to firstorder, a function of light intensity, but only of the wavelength of thelight traveling through the medium. For example, in the case of anoptical medium with positive dispersion, light at 1550 nm will travelthrough the optical medium more quickly than light at 1300 nm.

FIGS. 16-18 show a series of traces that illustrate the currentembodiment.

FIG. 16 shows a schematic of a) the electric field of a single laserbeam, both in time and space (1600). b) the electric field of a pulsetrain created when a second laser, of a different wavelength, is madeco-propagating with the first (1610). In the example of FIG. 16, thewavelength of the second beam is 85% the wavelength of the first. Thiswould be the case if the wavelength of the first laser was 1550 nm andthe wavelength of the second laser was 1317.5 nm.

FIG. 17 shows a schematic of a) the electric field of a single laserbeam, both in time and space, when we have introduced a phasemodulation, of 0.5 radians peak (1700). b) the electric field of a pulsetrain created when a second laser, of a different wavelength like thatin FIG. 16, is made co-propagating with the first and in the case wherewe have introduced a phase modulation, of 0.5 radians peak (1702). c) Agraphic of the magnitude of the induced phase modulation, in time andspace (1704).

FIG. 18 shows a schematic of a) the electric field of a single laserbeam, both in time and space, when we have introduced a phasemodulation, of 0.5 radians peak, and dispersion, ˜2%, to the model(1800). b) the electric field of a pulse train created when a secondlaser, of a different wavelength like that in FIGS. 16 and 17, is madeco-propagating with the first and in the case were we have introduced aphase modulation, of 0.5 radians peak, and dispersion, ˜2% (1802). c) Agraphic of the magnitude of the induced phase modulation, in time andspace (1804). d) the integral of equivalent phase space window, 36radians in space and 40 radians in time due to the refractive index usedin the model, in both time and space for the pulse train shown in 18 b)(1806). It can be seen from 18 d) (1806) that, although the integralthrough space, for the given phase space window, is zero at any giventime, the integral through time, for the given phase space window, isnon-zero at some spatial positions.

FIG. 18 illustrates that, when dispersion is present and consequentlythe two lasers travel through the optical medium at different speeds,each successive pulse manifests in a different phase, linearlyincremented from the previous pulse. This, in conjunction with judiciousphase modulation, affords the opportunity to arrange the constructiveand destructive interferences to selectively/preferentially reoccur in agiven spatial location.

As an example, if we were to measure the electric field at a locationnear the middle of the second, spatial, trace in FIG. 18 d), a locationwhere the time integral is positive, we would measure a net, positive,electric field as a function of time.

If we were to place a charge at the above location, near the middle ofthe second, spatial, trace in FIG. 18 d), a location where the timeintegral is positive, that charge would experience a net force,proportional to its charge and the net magnitude of the electric fieldmanifested at the selected position. Additionally, if we placed a chargeof opposite sign at a location near the ¼ point of the second, spatial,trace in FIG. 18 d), a location where the time integral is negative,that charge would experience a net force, proportional to its charge andthe magnitude of the electric field manifested at that selectedposition.

In this example, the spacing between adjacent maxima and minima in FIG.18 d) is 9 times the wavelength of the laser used in the schematic andthat the schematics are to scale in the time and spatial dimensions.This means that, in the case of a ˜1.5 um laser, the adjacent maxima andminima in FIG. 18 d) would be ˜13 um, well within the manufacturingcapabilities of modern IC, and even TFT, processes. This, as well as theabovementioned device availability, affords a strong opportunity toexploit the present embodiment on practical device scales.

The goal of the present embodiment is to create conditions wherein theintegral through time, for a given phase space window, is non-zero atsome spatial positions. Below, we draw note to some degrees-of-freedom,not apparent in the figures, that can facilitate those conditions.

1) A laser's phase is modulated asynchronously to its own phase. Thiscan be accomplished when a first set, of two, lasers is configured togive rise to a pulse train which modulates the refractive index of theoptical medium, while a third, laser (e.g. crossed with, but notco-propagating with the first two) experiences the induced phasemodulation. Since each laser, of the three, can have a differentwavelength, (e.g. the third laser has a wavelength of 1550+1 nm) thephase of the third laser can be uncorrelated with the induced phasemodulation generated by the first two lasers.

2) The third laser's amplitude is modulated apart-and-separate from thephase modulation. This can be accomplished by either electronic oroptical means. An example of the optical case would be a fourth lasersource (e.g. 1317.5+2 nm) made to be co-propagating with the thirdlaser, discussed in 1), above. If the fourth laser is of equal power,the pairing would result in a pulse train, but if the power levels areoffset (e.g. the fourth laser having substantially lower power than thethird), the amplitude modulation can be tuned to optimize the desiredeffect.

FIG. 19 shows a schematic illustrating one embodiment of the presentinvention.

A single longitudinal mode (SLM) laser, Laser I (1900), is directedthrough a beam combining optic (1902) and into an optical medium (1904)chosen with specific dispersion and non-linear optical susceptibility(i.e. optical Kerr effect). Laser I (1900) is then aligned to beproximate to a small charge carrier (e.g. microns in width) (1906). Asecond SLM laser, Laser II (1908), is routed with beam steering optics(1910), reflected off the beam combiner (1902), and aligned to beco-propagating with the first laser (1900). In this embodiment, Lasers I(1900) and II (1908) give rise to a pulse train and consequently aperiodic modulation of the index of refraction in the optical medium(1904).

A third SLM laser, Laser III (1912), is directed through a beamcombining optic (1914), routed with beam steering optics (1916), andmade to cross with Lasers I (1900) and II (1908) within the opticalmedium (1904), proximate to the charge carrier (1906). In thisembodiment, Laser III (1912) is configured to experience the periodicmodulation of the index of refraction within the optical medium (1904)created by Lasers I (1900) and II (1908).

A fourth laser, Laser IV (1918), is routed with beam steering optics(1920), combined with Laser III (1912) with beam combiner (1914), andaligned to be co-propagating with Laser III (1912). In this embodiment,Laser IV (1918) is used to modulate the amplitude of Laser III (1912),through constructive and destructive interference, to optimize the forcemeasured upon the charge carrier (1906).

The interferometric force detection system is similar to that describedearlier in this submission. A fiber optic force detection system similarto that used in atomic force microscope studies (D. Rugar, H. J. Mamin,and P. Guethner, Appl. Phys. Lett. 55, 25, (1989) 2588) is employed hereto measure force induced between a wire cantilever charge carrier (1906)and a laser beam (1912).

The output of a single-mode fiber-coupled probe laser (1922) is directedinto a single mode 2×2 fiber coupler (1924). One optically cleaved endof the output fiber (1926) of the fiber coupler (1924) is positioned inclose proximity (e.g. single microns) and perpendicular to the wirecantilever (1906). A piezo electric actuator, PZT (1928) is attached tothe optical fiber (1926) and driven by a signal generator (1930). ThePZT (1928) drives the motion of the optical fiber (1926) perpendicularto the wire cantilever (1906).

The single frequency laser light exiting the output of the fiber coupler(1926) is made incident upon the wire cantilever (1906). A portion ofthe light exiting the optical fiber (1926) and incident on the wirecantilever (1906) is reflected back into the optical fiber (1926) andco-propagates with the light reflected from the internal surface of theoptically cleaved fiber (1926).

The return signal, the optical interferometric signal between thecounter propagating reflection of the optically cleaved end of theoptical fiber (1926) and the reflective surface of the wire cantilever(1906), travels back through the optical fiber (1926), back through thefiber coupler (1924), and is directed into a detector photodiode (1932).The output of the detector photodiode (1932) is measured using a lock-inamplifier (1934), using the reference signal from the signal generator(1930) driving the PZT (1928). The signal from the lock-in amplifier(1934) is observed on a monitor oscilloscope (1936). A monitorphotodiode (1938) can be employed to measure the second output of thefiber coupler (1924) to ensure system stability.

The constructive and destructive interference between the lightreflected from the internal surface of the optically cleaved fiber(1926) and the light reflected from the wire cantilever (1906), drivenand detected at the frequency of the lock-in amplifier (1934), allowsfor a very sensitive detection of movement of the wire cantilever (1906)(e.g. nanometers). When the wire cantilever (1906) is chosen with asmall force constant, this allows for very sensitive force detection(e.g. nanoNewtons).

FIGS. 20-24 show a series of images that illustrate the currentembodiment, per FIG. 19.

FIG. 20 shows a gray-scale image of the electric field intensity of asingle laser beam (e.g. laser III (1912) in FIG. 19) plotted both inspace and time. In the gray-scale image, black represents an electricfield pointed into the plane of the page (relative field intensity equalto minus one) and white represents an electric field pointing out of theplane of the page (relative field intensity equal to plus one). In FIG.20, the model includes no phase modulation and no dispersion. Theelectric field anti-nodes are diagonal in the image, denoting and ‘equalspeed/frequency’ in both space and time.

FIG. 21 shows a gray-scale image of the electric field intensity of asingle laser beam (e.g. laser III (1912) in FIG. 19) plotted both inspace and time. In FIG. 21, the model includes no phase modulation, butintroduces ten percent optical dispersion. The electric field anti-nodesare no longer diagonal in the image, but compressed in the spatialdirection, x, denoting reduced speed in space.

FIG. 22 shows a gray-scale image (2200) of the electric field intensityof a single laser beam (e.g. laser III (1912) in FIG. 19) plotted bothin space and time. In FIG. 22, the model includes both phase modulationand optical dispersion. The phase modulation induced in the sample (e.g.by lasers I (1900) and II (1908) in FIG. 19) are shown in time (2202),for x=0, and space (2204), for t=0, in FIG. 22. We note here that, sincethe lasers (1900 and 1908) giving rise to the phase modulation (2202 and2204) are separate and distinct from the laser (1912) shown in thegray-scale image (2200) the phase modulation (2202 and 2204) is notcorrelated, in time or space, to the phase state of electric field shownin the gray-scale image (2200).

FIG. 22 also shows the integral, in both time (2206) and space (2208)for the electric field shown in the gray scale image (2200). It can beseen that, although the integral through space (2208) for the phasespace window indicated, is zero at any given time, the integral throughtime (2206), for the given phase space window, is non-zero at somespatial positions. FIG. 22 illustrates that, with judicious choice ofdispersion, amplitude modulation, and phase modulation (e.g. FIG. 19),we can arrange conditions such that a propagating electric field (e.g.laser III (1912) in FIG. 19) can selectively/preferentially manifest ina given spatial location.

FIG. 23 shows a gray-scale image (2300) of the electric field intensityof a single laser beam (e.g. laser III (1912) in FIG. 19) plotted bothin space and time. In FIG. 23, the model includes both phase modulationand optical dispersion, but, as a visual aid, the phase modulation isexaggerated verses that shown in FIG. 22. The phase modulation inducedin the sample (e.g. by lasers I (1900) and II (1908) in FIG. 19) areshown in time (2302), for x=0, and space (2304), for t=0, in FIG. 23.FIG. 23 also shows the integral, in both time (2306) and space (2308)for the electric field shown in the gray scale image (2300). It can beseen that, although the integral through space (2208) for the phasespace window indicated, is zero at any given time, the integral throughtime (2206), for the given phase space window, is non-zero at somespatial positions.

In FIG. 23, the effect is more visually apparent than in FIG. 22. InFIG. 23 the broad, black, features in the gray-scale image, indicatingareas where the electric field points into the page, can be seen tocorrespond with the area of negative net electric field in the timeintegral plot (2306). Also, the broad, white, features in the gray-scaleimage, indicating areas where the electric field points out of the page,can be seen to correspond with the area of positive net electric fieldin the time integral plot (2306). This more clearly illustrates that,with judicious choice of dispersion, amplitude modulation, and phasemodulation (e.g. FIG. 19), we can arrange conditions such that apropagating electric field (e.g. laser III (1912) in FIG. 19) canselectively/preferentially manifest in a given spatial location.

FIG. 24 shows a gray-scale image (2400) of the electric field intensityof a single laser beam (e.g. laser III (1912) in FIG. 19) plotted bothin space and time, similar to that of FIG. 22. In FIG. 24, the modelincludes both phase modulation and optical dispersion, like that in FIG.22. FIG. 24 also shows the integral, in time (2402) for the electricfield shown in the grayscale image (2400). It can be seen from thisfigure that the electric field integral through time (2202), for thegiven phase space window, is non-zero at some spatial positions.

FIG. 24 also illustrates how the non-zero electric field integral can beused to induce a net force on a target sample. FIG. 24 shows theplacement of a set of charge carriers (2404), along the ‘x’ direction oflaser propagation. The charge carrier with a positive electric charge isplaced to correspond with the location that manifests a positiveelectric field integral (out of the plane of the page). The chargecarrier with a negative electric charge is placed to correspond with thelocation that manifests a negative electric field integral (into theplane of the page). In such an arrangement, both charge carriers wouldexperience a force in the same direction (e.g. into the plane of thepage). The net force upon a sample with an array of suitably placedcharge carriers will be additive, so a net motive force upon the chargecarrier sample can be achieved with a set of lasers and carefulselection of dispersion, amplitude modulation, and phase modulation.

FIG. 25 is a flowchart of a method 2000 in accordance with another novelaspect. In a first step (step 2010), a first electromagnetic field isgenerated using a charge carrier. The charge carrier is disposed at alocation in space. The charge carrier comprises one or more chargecarriers. For example, in FIG. 19, a charge carrier 1906 generates afirst electromagnetic field.

In a second step (step 2020), a second electromagnetic field isgenerated that has a non-zero time integral at the location of thecharge carrier. The second electromagnetic field interacts with thefirst electromagnetic field thereby producing a force on the chargecarrier. For example, in FIG. 19, a radiation source comprises lasers1900, 1908, 1912, and 1918. Each of lasers 1900, 1908, 1912, and 1918 isselectively controlled, singularly or in combination, to generate asecond electromagnetic field having a non-zero time integral at thelocation of the charge carrier 1906. The second electromagnetic fieldinteracts with the first electromagnetic field to produce a force on thecharge carrier 1906.

FIG. 26 is a flowchart of a method 2100 in accordance with another novelaspect. In a first step (step 2110), a radiation source is controlled togenerate an electromagnetic field having a non-zero time integral at afixed spatial location. The radiation source includes one or more lasersof varying wavelengths. In the example of FIG. 19, lasers 1900, 1908,1912, and 1918 operate as a radiation source to generate anelectromagnetic field that has a non-zero time integral at fixed spatiallocation. In this embodiment, the fixed spatial location is selected tobe the location of a charge carrier 1906.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A system comprising: a charge carrier thatgenerates a first electromagnetic field; and a radiation source thatgenerates a second electromagnetic field having a non-zero time integralat a location of the charge carrier, wherein the second electromagneticfield interacts with the first electromagnetic field thereby producing aforce on the charge carrier, wherein the radiation source is a laser orset of lasers, and wherein the radiation source is directed through anoptically conductive medium.
 2. The system of claim 1, wherein theoptically conductive medium exhibits an optical Kerr effect.
 3. Thesystem of claim 1, wherein the optically conductive medium exhibitsoptical dispersion.
 4. A system comprising: a radiation sourceconfigured to generate an electromagnetic field that has a non-zero timeintegral at a fixed spatial location, wherein the radiation sourcecomprises a plurality of lasers each having different wavelengths, andwherein the lasers are directed through an optically conductive medium.5. The system of claim 4, wherein the optically conductive mediumexhibits an optical Kerr effect.
 6. The system of claim 4, wherein theoptically conductive medium exhibits optical dispersion.